1. Field of the Invention
The field of the invention is that of single-component silicone sealants that are stable during storage in the absence of moisture and that crosslink, by polycondensation reactions catalyzed using a catalyst, into elastomers that adhere to various supports, while being accompanied by a release of alcohol and being carried out at ambient temperature (for example, 5 to 35° C.) and in the presence of water (for example, ambient moisture). These sealants are commonly known as “single-component alkoxy silicone sealants”.
2. Description of Related Art
Such sealants based on silicone elastomers are used in many applications, especially in the building industry, as a means of leakproofing, jointing, coating and/or assembling, among others. The rheological properties of these single-component silicone sealants (pasty form) are the subject of much attention in these applications. It is the same as regards their resistance to bad weather and to heat, their low-temperature flexibility, their ease of use and their rapid in situ crosslinking/curing in contact with moisture from the air.
It is known how to prepare compositions having these properties by mainly mixing diorganopolysiloxane polymer(s) having terminal alkoxyl groups, mineral filler(s), silanes substituted by particular hydrolyzable groups, adhesion promoter(s) and a curing (or crosslinking) catalyst.
The abovementioned polycondensation reactions are those where Si—OR bonds react together (the R substituent being an alkyl residue) in the presence of water while releasing an alcohol ROH.
Compositions of this type appear more particularly in U.S. Pat. No. 5,674,936 and U.S. Pat. No. 5,698,653. The compositions according to this prior art are formed by mixing a diorganopolysiloxane polymer having terminal alkoxyl groups, a siliceous mineral filler, a nonreactive diorganopolysiloxane polymer having terminal trialkylsiloxyl groups, a curing catalyst based on a tetraalkyl titanate and an adhesion promoter consisting of a tris[1,3,5-(trialkoxysilyl)alkyl]isocyanurate (in the case of U.S. Pat. No. 5,674,936) or of an epoxysilane (in the case of U.S. Pat. No. 5,698,653).
However, a difficulty with which a person skilled in the art finds himself confronted with is the stability during storage, in particular in cartridges, of an alkoxy type sealant before its use. The stability is further degraded when the temperature of the storage medium is high. This is also expressed, when they are used after a long storage (of 3 to 12 months), by a degradation of the application properties of the sealant. Among the important properties required for good application of the single-component alkoxy silicone sealant, mention may be made of the extrudability, the cure rate (crosslinking over at least 2 mm in 24 hours) and the mechanical strength properties such as the tensile strength and the modulus at 100% elongation. It is understood that these problems of storage stability in cartridges also cause major difficulties as regards the logistics required for the delivery of this type of product, especially in hot countries.
To overcome the problems of storage stability, U.S. Pat. No. 5,741,839 proposes adding, to the sealant, a stabilizer which is a carbodiimide while proving that a sealant prepared without this additive can no longer be crosslinked after storage for 24 hours at 100° C.